The present invention is directed to telecommunications bay maintenance and more particularly to a circuit pack latching system.
The maintenance of telecommunications bays requires the periodic extraction and insertion of major components called circuit packs. At the backplane end of a circuit pack are thousands of connector pins surrounded by an electromagnetic compatibility (EMC) gasket.
When inserting a circuit pack into its bay, these connector pins engage their respective pin holes requiring an increase in insertion force to overcome the opposing force as the pins encounter their pin hole walls.
As advances have been achieved in circuit pack technologies there has been a resultant increase in pin density, and as pin densities increase the required insertion force increases correspondingly. One way to overcome these increases is to have the installer apply more manual force. However, a preferred solution would be to provide an increase in insertion force without requiring an increase in applied manual force.
One way to provide increased insertion force without requiring increased manual force is to provide a levered latch that has a longer arm for increased leverage. However, because latches are typically located on circuit pack faceplates, a longer arm would present difficulties since circuit packs have limited faceplate real estate, most of which is required for optical interconnects and LEDs. As well, longer arms would stick further out into aisle space when open, presenting a safety hazard and an increased risk of latch damage.
In addition to the force required to insert the pins, an additional force is required to compress the EMC gasket. The gasket maintains an EMC seal between the circuit pack and the backplane when the circuit pack is installed. In order to maintain a proper EMC seal the gasket is compressed in the last few millimeters of circuit pack insertion and its opposing force is compounded with the opposing pin force as the backplane end of the circuit pack approaches the backplane.
As well, the force required to compress an EMC gasket increases the more it has been compressed, wherein more and more force must be applied as the circuit pack approaches the backplane.
Another characteristic of EMC gaskets to be considered is known as xe2x80x9cforce relaxationxe2x80x9d, which occurs as the gasket shrinks over time, potentially leading to the loss of a proper EMC seal. In order to compensate for it, force relaxation should be taken into consideration.
Therefore, with the cumulative effect of higher and higher pin densities, compounding resistance forces and force relaxation, what is needed is a latch that provides for an intensifying insertion force without requiring a corresponding increase in applied manual force, does not take up large amounts of faceplate real estate and continues to provide available insertion force to take up tolerance that may occur due to force relaxation.
For the foregoing reasons, there is a need for an improved method of latching circuit packs.
The present invention is directed to a variable insertion force circuit pack latching system and method. The system includes a latch assembly mounted on the front of a circuit pack and adapted to couple to a trough block mounted on a bay frame, the trough block having a hook-shaped tongue adapted to conversely couple to the latch assembly to secure the circuit pack in the installed position.
The latch assembly includes a base mounted on the circuit pack front using a base fastener fastened through a traversing channel formed within the base, and the base adapted to slide laterally across the circuit pack front. The latch assembly further includes a lever having a long arm and a short arm, the lever hinged-mounted to the base at about the joint of the two arms, the lever having a surface that interacts with the trough block to cause the short arm to couple with the trough block.
The latch assembly further includes a retraction spring attached at one end to the circuit pack side of the short arm of the lever towards the lever pivot point end of the short arm, and at the other end to the base fastener so that, as the latch assembly slides past the trough block during circuit pack insertion, the spring holds the latch assembly retracted within the plane of the circuit pack front until the latch assembly is activated and begins coupling with the trough block. The latch assembly further includes a catch affixed to the long arm end of the base and adapted to secure the long arm to the base once the pin connectors are fully engaged and the gasket is compressed.
In an aspect of the invention, the trough block is mounted to the bay frame using one or more fasteners and includes a spring element that provides a spring force between the hook-shaped tongue of the trough block and the bay frame about equal to the force required to insert the circuit pack. In this way, the spring element has an ability to compress to take up tolerance between the circuit pack and the backplane that may occur due to force relaxation in the gasket or the bottoming-out of the backplane connectors.
The invention provides a gain in mechanical advantage as opposing forces compound during the final phase of circuit pack engagement.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.